The present invention relates to an arrangement of electrochemical cells, in particular an arrangement of batteries or capacitors which are connected in series or in parallel and which include additional electrical circuit elements or additional electrical circuitry.
In recent years there have been large advances in the design and production of batteries. In particular, lithium-ion batteries provide many advantages over conventional nickel cadmium batteries. Lithium-ion batteries can be formed by flattened xe2x80x9cjelly-rollsxe2x80x9d of interleaved electrodes and electrolyte, the thus formed electrical cell being packaged in a flexible pack formed, for example, from thin laminated foil material. The ability to seal the cells within flexible housings, rather than the traditional rigid cans, is based on the fact that the lithium-ion batteries use a gelled or solid polymer electrolyte. The problems relating to leakage, which are known in connection with conventional batteries, do thus not arise.
The widths and lengths of polymer, lithium-ion cells can be freely selected, as can the thickness of the cells. This flexibility of design, and the flexibility of the finished cell, makes polymer lithium-ion cells particularly suitable for use in portable telephones and computers, as well as in other electronic devices where space is at an absolute premium. It will be well understood that a compromise must often be reached between the energy to be delivered by a battery and the space available for the battery.
Examples of lithium-ion cells construction and the use of flexible packages for such cells are described in more detail in, for example, WO-A-97/03475 (Danionics), EP-A-0845821 (Sanyo) U.S. Pat. No. 5,609,974 (Battery Engineering), U.S. Pat. No. 4,997,732 (MHB), U.S. Pat. No. 5,476,668 (Bell), WO-A-95/13629 (Valence), U.S. Pat. No. 5,591,540 (Motorola), U.S. Pat. No. 5,716,421 (Motorola) and U.S. Pat. No. 5,445,856 (Gill).
The operational voltage of lithium-ion batteries is typically 3 to 4 volts. On the other hand, the voltage demand of many electronic devices is 8 to 9 volts, or some other multiple of the individual cell voltage. Thus, it is commonplace for lithium-ion cells to be arranged one adjacent the other, and connected in series. Alternatively, the cells can be placed one on top of the other, and again connected in series. In different situations, it is possible that a higher capacity is required, for the same voltage, in which case a number of cells could be connected in parallel.
When a number of cells are connected in series, it is generally necessary to provide some voltage equalizing components across each cell, to avoid the problem of the charging voltage being applied unequally between the individual cells, which would result in an unequal load on the individual cells so reducing the performance and lifetime of the cell. The voltage equalizing components are typically resistors. However, it is also commonplace for other electrical components to be connected to the cells, e.g. capacitors, integrated circuits for charge control, state of charge indicators, memory elements, disconnect switches and other associated control circuits. Usually, such additional circuit elements and circuitry are arranged at the end of the stack or row of individual cells, adjacent the terminals. The additional circuit elements and circuitry obviously need some protection and this is usually done by providing a hard box for the arrangement of cells and circuit elements, contacts being provided on the external surface of the hard box.
However, while in such arrangements a saving of space is achieved relative to traditional cells, there is an ever present demand for further space saving so that the maximum energy density can be achieved, particularly for cells to be used in mobile phones etc.
It should be emphasized that the present application, and the issues discussed above, apply equally to electrochemical capacitors as to batteries. The design of such electrochemical capacitors is similar to that of lithium-ion cells. An example of such a capacitorxe2x80x94sometimes known as a xe2x80x9csuper capacitorxe2x80x9d xe2x80x94is described in more detail in U.S. Pat. No. Pat. 5,646,815 (Medtronic) or in EP-A-0625787 (Matsushita). Generally speaking, electrochemical capacitors, either based on the double layer principle or on the pseudo-capacitance principle, differ from batteries in providing high discharge rates over a short length of time, whereas batteries are better suited to providing a power output over a longer period of time. Electrochemical capacitors also tend to be able to be recharged many more times than batteries. In some situations, the capacitors can replace batteries and in other situations they can be used together with batteries, for example as load levelling devices.
The capacitors can also be used as memory back-up elements in electronic devices, and in mobile transmitting equipment, for example in connection with mobile telephones where there is a demand for high current rate pulses. In this context, therefore, a combination of capacitors and high density battery cells is often required.
The operational voltage of a double layer supercapacitor is typically 2 to 3 volts. For the same reasons as discussed above in relation to battery cells, it is frequently necessary to connect a number of electrochemical capacitors together, in series or in parallel. As indicated above, it is also often necessary to connect a combination of battery cells and electrochemical capacitors together. Again, these groups of cells will tend to include electrical components and electronic circuits, which typically would be housed altogether in a hard box, thus providing protection for the circuitry.
Electrochemical cells, either batteries or capacitors, are often produced as relatively thin square or rectangular cells, as described in the above-mentioned U.S. Pat. No. 5,445,856. In the present application these cells are called xe2x80x9cflat cellsxe2x80x9d and this term is intended to cover cells whose thickness is substantially less than the width and/or length of the cells. Because of the production method of the cellsxe2x80x94often by winding strips of electrodes and electrolytexe2x80x94the cells will be square or rectangular in shape. The term xe2x80x9cflat cellsxe2x80x9d will thus normally be understood to mean relatively thin square or rectangular cells, though the invention is not limited to a square or rectangular shape.
In U.S. Pat. No. 5,637,418, an electrochemical cell stack is described in combination with a flexible circuit board. In the patent, the circuit board is folded around the electrochemical cell stack.
U.S. Pat. No. 5,367,431 describes a thin power supply unit with flat power supply elements bonded onto a flexible circuit board. In one embodiment, power supply elements are arranged on both sides of the circuit board. Electrical connections between the elements and the circuit board are established by means of openings in the cases of the elements.
It is an object of the invention to provide an arrangement of electrochemical cells and associated electrical components and/or electronic circuitry in which the said components/circuitry can be protected and wherein a relatively high saving of space can be achieved.
According to the invention there is provided a cell unit including at least two flat electrochemical cells which are connected with additional electrical components and are connected together, the cells being folded such that the external terminals of the cell unit are exposed but that the additional elements are positioned between the cells. The components may be positioned between the faces of the cells, when folded together, or between the edges of the cells.
In another aspect of the invention, there is provided a cell unit which includes at least two flat electrochemical cells and a circuit board, the cells being folded onto one or both sides of the circuit board whereby the circuitry on the circuit board is protected. If the circuitry is provided on only one side of the circuit board then the cells can be folded only onto that one side. If circuitry is provided on both sides of the circuit board then preferably the cells are folded onto both sides of the board.
Preferably, the cells and the circuit board are square or rectangular. Cells can be provided on two or more sides of the circuit board and two cells can be connected at each side of the board.
It will be understood that the flat cells which are housed in relatively soft flexible packaging provide a high degree of protection to the circuit elements or circuitry, particularly bearing in mind that the relative flexibility of the cells means that any shocks transferred to the cell unit are at least partly absorbed and are not fully transferred to the circuit elements or circuitry on the circuit board.